1. Field of the Invention
The invention relates to a metal foam jointing method, a preformed body composite formed by foaming a metal foam material, and a jointing clamp for clamping the preformed bodies to be joined.
It is especially true in lightweight structural engineering that there has always been a problem in joining individual structuresxe2x80x94termed preformed bodies in the followingxe2x80x94in keeping with the requirements of the later application, not least due to the demand for low weight while at the same time ensuring high mechanical loading capacity and stability at low cost. This is also basically a problem in other fields, for instance, in shipbuilding where particularly large-area preformed bodies, for example hull segments, need to be joined to each other, although here too, there is always the requirement for the smallest deadweight possible while assuring high mechanical loading capacity of such preformed bodies and the composite bodies composed thereof.
2. Description of Related Art
One possibility of saving weight is to make use of preformed bodies of foamed metal foam material or proportions of such materials. Due to the cellular structure of its frothed metal foam, a foamed metal preformed body has a lower weight than a preformed body produced from the solid while still assuring high mechanical loading capacity. Aside from this, metal foam material features a whole series of advantageous properties, such as, for instance, high shock absorption, noise absorption, as well as reduced heat conductivity and electrical conductivity as compared to the solid material. Metal foam materials and slabstock and preformed bodies produced therefrom are known, for example, from DE 41 01 630 C2, DE 43 18 540 A1, DE 44 16 371 A1, DE 44 26 627 A1, DE 196 12 781 01 C1 and DE 197 17 894 A1. Proposed in DE 43 18 540 A1 is the use of metal foam material in automobile production, in which body panels are employed as foamed metal preformed bodies, comprising a solid metal skin and a foamed layer of metal foam. For securing fitted items to these body panels, mention is made of self-cutting screws and dowel-type fasteners. DE 196 12 781 01 C 1, likewise, relates to preformed bodies for motor vehicles. In the publication xe2x80x9cMetallschaume 1997xe2x80x9d, MIT Bremen, the paper xe2x80x9cJoining of Aluminum Foamsxe2x80x9d by N. Sedliakova et. al. describes screw fasteners, soldered, cemented and welded joints as well as the use of fasteners foamed-in-place as methods for joining foamed metal preformed bodies. These are the accepted methods for joining preformed bodies, the advantages and disadvantages of which are well known in engineering.
An object of the present invention is to provide a particularly secure composite of preformed bodies and to provide the jointing technique required therefore.
In accordance with the invention, preformed bodies are compacted into a solid composite body in a jointing method with the aid of a metal foam material. For this purpose, in a first step, the preformed bodies to be joined are located fixedly relative to each other in positions as desired for the composite, preferably by being clamped to each other. In their jointing zone, use is made of a jointing clamp to define a space, more particularly a cavity, to thus form an encasement in which foamable metal foam material is arranged. The metal foam material may be introduced into the space encased by the jointing clamp either prior to, during, or after joint clamping. In a second step, the foamable metal foam material is foamed, this being preferably done by heating it to the foaming temperature of the metal foam material. Due to the increase in volume of the metal foam material involved in foaming and the definition thereof by the sufficiently solid encasement, the preformed bodies are compacted into a composite body.
In a preformed body composite in accordance with the invention, the preformed bodies are joined together by means of a jointing clamp which forms an encasement for a metal foam material foamed in producing the composite. The jointing clamp defines a space, at least in part, in which the metal foam material is able to expand in foaming. Due to the increase in volume of the metal foam material into the limits dictated by the encasement, the preformed bodies are compacted into a composite.
In a first preferred embodiment, a prefabricated separate jointing clamp is employed as the jointing clamp. This separate jointing clamp is placed on the preformed bodies to be joinedxe2x80x94the preformed bodies having been preferably arranged matching each other in the shape of the later compositexe2x80x94by it clasping the preformed bodies or at least parts thereof. In this arrangement, the jointing clamp may already clampingly locate the preformed bodies to be joined together in the desired position relative to the composite. A non-clamping application of the jointing clamp is likewise possible, however.
In accordance with a second preferred embodiment, the jointing clamp is formed by the corresponding configuration of the preformed bodies themselves so that applying a separate jointing part, preferably the aforementioned separate jointing clamp, may be eliminated. In this case, the jointing clamp is an integral component of one of the preformed bodies or is formed in the cooperation of the preformed bodies.
The foamable metal foam material may be a constituent of one, several or all preformed bodies involved in the composite, Thus, a preformed body, used preferably, is fabricated from a slab of laminated material comprising at least one layer of a foamable metal foam material and an adjoining skin of a metallurgically compatible solid metal material. From such a semi-finished product, a preformed body in the sense of the invention is produced by known forming methods, more particularly cold forming. Typically, the foamed material and solid material is formed each by the same metal or the same metal alloy, for example, foamable aluminum foam and solid aluminum. However, any compatible, unlike pairing of materials is just as usable for the purposes of the invention, the foaming temperature of the foam material being preferably below the melting temperature of the solid material. The foam material of one or more preformed bodies may be foamed even prior to jointing. One or more of the preformed bodies to be joined may also consist only of the metal foam material.
However, the invention is not restricted to application with preformed bodies containing foam metal materials, it also being applicable to advantage also with metallic preformed bodies having no foam material, for example as with conventional sheets of metal or other section or shell bodies. Preformed bodies obtained by sintering or casting, for example, may be involved. The invention is, although preferred, not restricted exclusively to joining metallic preformed bodies. In principle, any kind of preformed bodies may be joined into a composite in accordance with the invention by means of the jointing system in accordance with the invention, as long as these preformed bodies are not ruined by the foaming temperature of the foam material used in each case; preferably they should remain dimensionally stable at the foaming temperature.
The jointing clamp defines or encases in the jointing zone a space in which a supplemental section of a foamable metal foam material may be inserted before, during or after positioning of the jointing clamp. By inserting a suitable supplemental section, foam material may be incorporated in the jointing zone optimized in quantity and form as regards the foaming procedure and later compacted composite. In this way, should the preformed bodies to be joined not contain any foamable metal foam material themselves in the jointing zone, foam material is furnished at least by a supplemental section.
As a further, or also sole, means of introducing foamable metal foam material into the jointing zone, a prefabricated separate jointing clamp may also be used.
A separate jointing clamp in accordance with the invention comprises, in a tubular cylindrical section, a layer of a foamable metal foam material and a skin surrounding this foam layer, i.e. encasing the metal foam material of such a sandwiched foam layer during foaming. In its simplest embodiment, such a jointing clamp may be used like a sleeve for joining two abutting cylindrical preformed bodies. Preferably, the jointing clamp is provided with an opening in its tubular cylindrical section, however. The opening extends to advantage up to at least one face end of the tubular cylindrical section and in particular, it being configured preferably as a full-length opening so that the tubular cylindrical section of the jointing clamp is open throughout longitudinally. The separate jointing clamp may also be formed as a tubular section, in which at least one foamable supplemental section is inserted, which is foamed prior to jointing or in the course thereof and subsequently stiffens the tubular section of the jointing clamp.
In the embodiment provided with the opening, the separate jointing clamp is fitted, mounted, pushed in place or otherwise suitably fixedly located relative to the preformed bodies placed in accordance with each other on joining sections configured accordingly on the preformed bodies. In the starting position prepared for foaming, joining sections of the preformed bodies to be jointed thus protrude into the cavity defined by the jointing clamp. Preferably, a joining section protrudes into the space encased by it also when a jointing clamp is configured integrally. A joining section of a preformed body may be formed at one edge of the preformed body or also at any other joining location of the preformed body serving to make the joint.
The preformed bodies may also be held together in the location desired in the composite by means of the jointing clamp, more particularly, by the separate jointing clamp.
In a likewise preferred aspect, clamps or other suitable fixing means for locating the preformed bodies relative to each other may be used in addition to the jointing clamp, which may be configured separately or integrally.
The jointing material used in accordance with the invention, namely foamable metal foam material, may be included in the jointing zone by the preformed bodies themselves to be joined, by a separate jointing clamp or by one or more supplemental sections. To particular advantage use is made of combinations of these foam metal inclusions, more particularly a combination of all three possibilities.
Should more than two preformed bodies abut in a common jointing zone, such a preformed body composite may be produced particularly simply by using a separate jointing clamp. The jointing clamp provided for this purpose may be formed for example by a star-shaped jointing clamp tubular section.
Since the foam material comprises a cellular structure in the jointing zone during and after foaming, and thus, as is known, has a reduced heat conductivity as compared to that of the solid material, the jointing zone, i.e. the space encased by the clamp, is thermally treated from within. In addition to cooling in terminating foaming or for accelerated cooling after foaming, it may be of advantage to internally heat the foam material for the purpose of foaming. The thermal treatment means for cooling, or for heating, or also for cooling and heating, may be formed in principle by any suitable cooling or heating means, for example by the application of electrical energy. Preferably, the thermal treatment means is formed, however, by at least one flow conduit, through which the cooling or heating fluid is guided. The flow conduit may be perforated to bring the thermal treatment means into direct contact with the foam material.
In another preferred aspect, the metal foam material is charged from within by a fluid, preferably an inert gas or reaction gas, by means of which the oxidative effect of a foaming agent contained in the foamable metal foam material is reduced or increased. A perforated flow conduit, arranged for this purpose in the jointing zone, may be formed by the aforementioned thermal treatment conduit, although, a separate further conduit having small openings, i.e. a perforated conduit, may be incorporated.
The thermal treatment fluid and the fluid for controlling an oxidation may be formed by one and the same fluid.